A unit cell which is a minimum electric generating cell unit of a prior art solid polymer electrolyte type fuel cell having a flat-plate structure (hereinafter referred briefly to “flat-type fuel cell” in some cases) generally has a membrane electrode assembly in which catalytic electrode layers are connected to both sides of a solid electrolyte membrane. Further, gas diffusion layers are disposed on both sides of the membrane electrode assembly. Further, separators each having a gas flow passage are disposed on outer sides of the gas diffusion layers. The separator functions to flow a fuel gas and an oxidant gas fed into the catalytic electrode layers via the gas-diffusion layers and to conduct an electric current obtained by electric generation to the outside.
In order to miniaturize the flat-type fuel cell and enlarge the electric generating reaction area per unit volume, the thicknesses of the constituting members of the flat-type fuel cell need to be small. In such conventional flat-type fuel cells, it is not preferable from the standpoint of the function and the strength to make the thickness of each constituting member small to a certain value or less, so that they are reaching the design limit. Under the circumstances, tubular or columnar fuel cells in which respective layers constituting the fuel cell are laminated coaxially have been developed.
For example, Patent document 1 discloses a tube-type fuel cell in which an inner current collector, an inner catalytic electrode layer, a solid electrolyte membrane, an outer catalytic electrode layer, an outer current collector are provided coaxially and in sequence order from the inner side. This tube-type fuel cell has gas flow passages on the outer peripheral face of the inner current collector and on the inner peripheral face of the outer current collector. Since such tube-type fuel cells can be closely arranged in a given space when the diameter of the fuel cells is smaller, the electrode area per unit volume can be largely increased as compared with the conventional flat-type fuel cell.
For example, a method for manufacturing such a tube-type fuel cell includes sequentially providing, on an inner current collector, an inner catalytic electrode layer, a solid electrolyte membrane, an outer catalytic electrode layer, and an outer current collector in this order. Specifically, such a method includes applying an inner catalytic electrode layer forming-composition to the inner current collector, drying the composition to form the inner catalytic electrode layer on the outer peripheral face of the inner current collector, and forming the solid electrolyte membrane and the like by similar methods so that the tube-type fuel cell is formed in sequence. In this method, the catalytic electrode layer and the like are formed by coating. Therefore, this method has the advantage that a tube-type fuel cell with good adhesion between adjacent layers can be obtained.
However, the above method has the problem as follows. Since gas flow channels are formed on the outer peripheral face of the inner current collector, the application of the inner catalytic electrode layer forming-composition thereto causes a problem in which part of the composition enters and blocks the gas flow channels.
Patent Document 1: Japanese Patent Application Laid-Open No. 2002-124273
Patent Document 2: Japanese Patent Application Laid-Open No. 09-223507.